Field of the Invention
The present invention relates to a method for performing a mobile user terminal route update in a telecommunication network operated based on the Internet Protocol.
In the future the telecommunication networks and particularly the radio access networks thereof will change to adopt a complete Internet Protocol (IP) solution where the cellular base transceiver stations, herein also referred to as network transceiver device gateways, behave as “Last Hop Gateways” of the Internet towards the mobile user terminals. That is, they serve as entry and/or exit points to and/or from the Internet. The IP radio access network can be considered as an autonomous system which provides access to the Internet by using the mobile user terminals.
The basic assumption underlying the current standardization activities of the “MobileIP” workgroup is that the mobile user terminal must be able to communicate using the same IP address at all times, regardless of its point of access to the Internet.
At the moment IPv4 addressing scheme is in use and it will be replaced with IPv6 addressing scheme in future, which will solve the address space problem of the IPv4 addressing scheme for the foreseeable future.
The mobile IP solutions with the IPv4 addressing scheme are rather complex and require the use of so-called tunneling, a Home Agent and a Foreign Agent because originally the Internet host computers were assumed to be connected only to their home network. That is, IPv4 packets must be tunneled if the terminal is connected to the Internet elsewhere than its home network.
In contrast thereto, the IPv6 addressing scheme will allow a mobile terminal host to host connection via Internet by using just terminal IP addresses throughout the network without any address conversions or tunneling, regardless of the mobile terminal host's current point of attachment to the Internet.
Within a radio access network (RAN) the mobile terminals (mobile user terminals) can move rapidly from one base station cell area to another base station cell area during an active connection (between a mobile user terminal and another fixed or mobile user terminal), so that then a handoff to a new serving base station must occur, that is, the IP packets arriving at the mobile user terminal must be directed to the new base station (Last Hop Gateway) in the IP radio access network (IP RAN).
It is to be noted that the expression “base station” as used herein is intended to mean a base transceiver station of the radio access network and is also referred to as network transceiver device gateway, as it represents the gateway in the sense of a kind of an interface from the mobile user terminals to the IP radio access network. Also, such a network transceiver device gateway is intended to mean a so-called Node B in case the radio access network conforms to the UMTS system as presently being defined in the 3rd generation partnership project (3GPP). Likewise, a user terminal may be a mobile user terminal (and/or a mobile terminal host also known as a mobile station) as well as a fixed user terminal (and/or host). Similarly as above, the expression user terminal is intended to be understood in its broadest sense, so that it covers also the case of a user equipment (UE) as a terminal device in a system conforming to UMTS as presently being defined in the 3rd generation partnership project (3GPP).
The handoff procedure must occur fast enough in order to prevent the generation of too long of a break in communications especially when there must be maintained a certain quality of service (QoS) like in a voice call.
As a result of the handoff procedure between base transceiver stations of the IP RAN, the destination of arriving IPv6 packets to the mobile user terminal must be changed in the routing elements of the IP RAN, i.e. the routing elements must be learned to forward packets to a new base transceiver station. On the other hand, the route from the base station towards a border gateway (of the IP RAN) via which the mobile user terminal (mobile host) communicates to a far-end host (fixed or mobile communication partner) must be changed in the routing elements of the IP RAN too, that is, both directions of connection must be updated in the routing elements of the network.
In this connection, it is to be noted that the expression routing element as used in this specification is to be understood in its broadest sense and is not limited to a specific type of routing element. A routing element is an element which routes and/or directs a flow of information between terminals connected to gateways and/or between gateways through an IP network which is present between the gateways. Particularly, the expression routing element means a Layer 3 switch as well as a so-called router, so that the present specification is valid for switched networks (comprising a layer 3 switch as a routing element) as well as for routed networks (comprising a router as a routing element). Also, if in this document reference is made to a mere “switch” as a routing element, this is of course meant to denote a Layer 3 switch as a routing element.
Depending on the IP RAN implementation by using a switched network or routed network, the route learning process (route update process) is somewhat different.
In the switched network solution, it is enough to send, towards the switched network, just one IP packet with the respective host's IP address as a source address via the gateways (transceiver gateway and/or border gateway) via which the hosts are communicating with each other via the IP RAN.
In the routed network solution, a routing table update message must be sent in order to update the new routing direction to the host's IP address.
However, due to fast packet switching requirement during a handoff process, known mechanisms for the route updating process in the IP RAN are not satisfactorily because they are still rather time consuming when compared to the packet switching times.
In all known IP radio access network solutions it becomes possible to implement the host to host connections via Internet by just using the mobile user terminal's IPv6 addresses throughout the network without any address conversions or tunneling, regardless of the mobile terminal's current point of attachment to the Internet.
In a tunneled host to host connection solution, the base stations behave as termination points to the tunnels which can be changed under control of the radio access network when a mobile terminal's point of attachment in the network is moving.
In a tunneled solution, however, there is drawback that the host to host connection IP datagrams must be encapsulated inside the datagrams of the tunneling protocol. This in turn increases the packet size of the datagrams which becomes a critical issue due to an extra overhead when quality of service (QoS) must be maintained in the services of the IP radio access network.
Therefore, it will be convenient to superannuate and/or to dispense with the use of tunneling when IPv6 addressing scheme is taken into use in the Internet.
Discarding the tunneling in host to host connections in the IP radio access network means easier connection management from the network point of view, but on the other hand, there will arise new problem situations in connection with the routing of IPv6 datagrams to the mobile hosts.
In a tunneled solution, the tunnel termination point IP addresses for the base stations are known by the network, that is, the routes to these are static in the involved routing elements of the IP radio access network.
Now, when mobile terminal's IPv6 address (an IP address associated thereto, i.e. its own one or a temporarily allocated one) shall be used, the problem is that a mobile host's point of attachment to the Internet must be informed to the routing elements of the network each time a handoff to a new location (new base transceiver station cell area) must be executed while the mobile host is moving during an active connection. Otherwise, the mobile host's correct location is temporarily unknown in the routing elements of the network while a handoff occurs.
The major problem in the IP radio access network handoff procedure is that IPv6 datagrams forwarded to the mobile host will be lost during establishing of the new wireless connection and setting up of the new route for the IP datagrams within the IP radio access network.
During a handoff procedure, the IP packets forwarded to and intended to arrive at the mobile host are routed to the base station to which the mobile host was “connected” (via the air interface) before handoff as long as the new route is not being informed to the routing elements of the network and their routing tables become updated.
Particularly, this problem becomes worse as the mobile host itself is active in this route updating procedure, that is, it is responsible for route updating control towards the network. In order to accomplish this, the mobile host must wait until the wireless connection to the new base station is established, which is the earliest moment when the mobile host itself is able to start route updating activities via the new base station, that is, the mobile host's new last gateway towards the IP Radio Access Network.
This means that route updating for the routing elements of the network by the mobile host's control can only occur far too late in order to avoid lost IPv6 packets during handoff procedure. Thus, inevitably some Ipv6 data packets will be lost due to handoff procedure and quality of service (QoS) will be degraded.
An earlier solution to the described problem can be found in the IETF draft “Mobile IP-Cellular IP-00”, which specifies a specific protocol that allows to route IP datagrams to a mobile host. The described protocol is intended to provide local mobility and handoff support. The introduced handoff solution is based on activities by the mobile host which transmits a route-update packet and redirects the packets destined for the involved mobile host from the old to the new base station.
The same assumption that a mobile host should be active in handoffs can be found also in the IETF drafts “Hierarchical Mobile Ipv4/v6 and Fast Handoffs” and “Mobility Support in Ipv6”.
However, imposing the burden of the route updating to mobile hosts in mobile IP does not fully conform with the conceptional idea underlying the Internet because the network should provide a transparent platform for host to host communications which is independent of the underlying network technology.